Helping people with computers... one answer at a time.
In practicality, information is deleted when it is deleted, although there are several scenarios where it could be recovered if someone were motivated enough!
I'd like to keep a copy of some conversations that I have in Yahoo Messenger; this is a feature that they offer and it's particularly handy if I want a reminder of the information given. The conversations are stored and I can access them through my Yahoo email account under my Inbox Conversations. However, sometimes this information is sensitive and after reading it, I go to my Conversations tab, look up the conversation, click on the box beside it and press Delete. Is the conversation actually deleted? If not, is there something that I can do to make sure that they are?
In this excerpt from Answercast #43, I look at the various ways that deleted information can be retrieved from a computer (but most of the time, no one will go to those lengths).
I'll answer the second part first: There's certainly nothing more that you can do.
Now, are the conversations deleted? Well, yes and no. Here's the problem – actually several problems.
One, the person at the other end could of course have kept their own record of the conversation; that you have exactly zero control over.
They could have a kept a copy and they could do whatever they want with that copy (including sharing it publicly), if they so desired.
So, even if you delete something from the current user interface to your mail, it's very possible that that information lives on in a backup that was taken last night, last week, last month.
Even worse, we don't know how long services like Yahoo actually keep their backups. They could keep them for a few weeks, a few months, a few years, or for all we know, forever. So in that sense, it's very difficult to say that it's absolutely, completely, irretrievably deleted.
Finally, even on your own computer, the fact that you've displayed this information in your web browser means it's very possible that the information is in your browser cache.
Then again (depending on exactly how sensitive this information is), you may want to run a secure delete utility to overwrite the area on which this information used to be written on your hard drive.
It seems like a bit much (and it is) but that's all the different ways that the information could be recovered – depending on exactly how motivated the individual trying to get the information really was.
In practice, in practicality, for the most part – people aren't that motivated. They don't go and get subpoenas to get old backups from your email service provider; they won't grab your hard disk and start trying to do data recovery on it.
It's not something that's going to be easy to get back. But if somebody's motivated sufficiently, then it's possible that they could. And, like I said:
Next from Answercast 43 – Is View Source a safe way to view suspicious emails?